Generally, films of aqueous polyurethane dispersions tend to become discolored on heat aging at temperatures up to about 150.degree. C., but are quite color stable at temperatures up to about 70.degree. to 100.degree. C. Vinyl chloride polymers on the other hand, are generally color stable, even at temperatures of 150.degree. C. for extended periods. When a vinyl chloride polymer is coated with an aqueous based (water soluble or dispersible) polyurethane, however, the composite discolors at temperatures as low as 70.degree. C.
In Hermann, U.S. Pat. No. 3,923,713, granted Dec. 2, 1975, it is proposed to add organic monoisocyanate, an antioxidant and a U.V. absorber to a urethane adhesive for plastic bonding to prevent gas-fade yellowing. Such use achieved a certain level of stability for the adhesive.
The art desired that a urethane as a coating be provided to a polyvinyl chloride or copolymer surface, which coating as well as the substrate would not discolor with extended use, or when subjected to high temperatures during and after the manufacturing process.
It is therefore a principal object of the present invention to provide a urethane coated polyvinyl chloride or copolymer in which discoloration at temperatures up to about 150.degree. C. is not a problem.
It is another object of the present invention to provide an improved method for coating a polyvinyl chloride or co-polymer surface with a polyurethane latex.
It is a further object of the present invention to provide certain treated urethanes in aqueous dispersion which can readily be coated on a polyvinyl chloride or co-polymer surface, and which are practical and aesthetically acceptable in use.